The transforming growth factor β (TGF-β) family of proteins includes the transforming growth factors-β (TGF-β), activins, bone morphogenic proteins (BMP), nerve growth factors (NGFs), brain-derived neurotrophic factor (BDNF), and growth/differentiation factors (GDFs). These family members are involved in the regulation of a wide range of biological processes including cell proliferation, differentiation, and other functions.
Growth/differentiation factor 8 (GDF-8), also referred to as myostatin, is a TGF-β family member expressed for the most part in the cells of developing and adult skeletal muscle tissue. Myostatin appears to play an essential role in negatively controlling skeletal muscle growth (McPherron et al., Nature (London) 387, 83-90 (1997), Zimmers et al., Science 296:1486-1488 (2002)). Antagonizing myostatin has been shown to increase lean muscle mass in animals.
Another member of the TGF-β family of proteins is a related growth/differentiation factor, growth/differentiation factor 11 (GDF-11). GDF-11 has approximately 90% sequence identity to the amino acid sequence of myostatin. GDF-11 has a role in the axial patterning in developing animals (Oh et al., Genes Dev 11:1812-26 (1997)), and also appears to play a role in skeletal muscle development and growth.
Activins A, B and AB are the homodimers and heterodimer respectively of two polypeptide chains, βA and βB (Vale et al., Nature 321, 776-779 (1986), Ling et al., Nature 321, 779-782 (1986)). Activins were originally discovered as gonadal peptides involved in the regulation of follicle stimulating hormone synthesis, and are now believed to be involved in the regulation of a number of biological activities. Activin A is a predominant form of activin.
Activin, myostatin, GDF-11 and other members of the TGF-β superfamily bind and signal through a combination of activin type II and activin type IIB receptors, both of which are transmembrane serine/threonine kinases (Harrison et al., J. Biol. Chem. 279, 28036-28044 (2004)). Cross-linking studies have determined that myostatin is capable of binding the activin type II receptors ActRIIA and ActRIIB in vitro (Lee et al., PNAS USA 98:9306-11 (2001)). There is also evidence that GDF-11 binds to both ActRIIA and ActRIIB (Oh et al., Genes Dev 16:2749-54 (2002)).
TGF-β protein expression is known to be associated with a variety of diseases and disorders. Therefore, therapeutic molecules capable of antagonizing several TGF-β proteins simultaneously may be particularly effective for treating these diseases and disorders.
Production of therapeutic proteins on a commercial scale requires proteins that can be efficiently expressed and purified without disruption of the integrity of the protein. Manufacturability can be described as the ability to express and purify a protein in a sufficiently efficient manner to allow for cost-effective production of the protein. In a commercial setting, manufacturability must be determined for each potential therapeutic protein. Although protein expression and purification processes can be optimized for a protein, manufacturability appears to be a function of the intrinsic properties of the protein as well. The present invention provides biologically active therapeutic proteins having improved manufacturability properties, capable of effectively antagonizing TGF-β proteins.